The June issue of Veterinary Forum magazine came, and was sitting on my desk (on top of the pile of journals and stuff). The cover illustration is the teaser for an article about treating pyoderma (Translation: Pus in the skin, or skin infections). It was really weird to have Star come in looking like she'd gone to the beauty-shop with her fashion magazine, saying "I want to look like this." Life imitates art.
The article is about treating deep skin infections, primarily those caused by surface skin bacteria that have gone crazy. Everybody has staph bacteria on their skin, but unless you scratch it open, or your immune system is lying down on the job, they just stay on the outside. When they go deep, it can take months to clear the infection.
Even if you pick an antibiotic to which the germ is sensitive (the magic bullet), it takes about three weeks to grow a new layer of skin. You won't clear these deep lesions with one week of treatment. If the problem is really severe, the patient will need antibiotics until looking good, and for 3 weeks afterward (or longer). Topical therapy with medicated shampoos and rinses are often required.
You also need to look for underlying causes. There is always a reason for this (though you may have trouble figuring out what that reason is). You check a skin scraping for mange mites, and make an impression smear cytology (smear the goo out and stain it, look at it under the microscope). Blood-work may reveal thyroid problems or other medical conditions that would lower the pet's resistance to infection.
A biopsy may be required to tell whether this is really an infectious process, or some other disease that the surface bacteria have simply used as an opportunity to enter. A portion of the biopsy (tissue that you remove for analysis) can be sent to be cultured to find out what germs are growing there, and what medications are best to treat them.
Skin conditions can rarely be diagnosed just from their outward condition. Star "looks just like the picture". However, her pen-mate is developing similar lesions. It isn't very likely that they both developed the same medical condition that allowed Staph bacteria to go crazy. In fact, we are looking at the possibility of Blastomycosis (a bad disease). False negative tests, multiple underlying causes, lots of possible reasons for the same outward appearance: it's why you don't find a lot of veterinary dermatologists around.